1. Field of the Invention
The present invention relates to a compressor, more particularly, to a compressor which secures a sufficient refrigerant inhaling passage so as to minimize a refrigerant inhaling resistance and also to increase lubricating action with respect to a thrust bearing supporting a swash plate, in a structure that refrigerant is inhaled to a cylinder bore through a hollow drive shaft, thereby improving the performance of the compressor.
2. Description of the Related Art
Generally, a compressor for vehicle inhales refrigerant gas which is vaporized and discharged from an evaporator and transforms it into refrigerant gas of high pressure and high temperature so as to be liquified easily and then discharges the transformed refrigerant gas to a condenser.
The compressor is classified into a swash plate type compressor in which a piston is reciprocated by rotation of a swash plate, a scroll type compressor which compresses refrigerant by rotation of two scrolls, a vane rotary type compressor which compresses the refrigerant by rotating vane and the like.
Among them, a reciprocating compressor which compresses the refrigerant by reciprocating of the piston further includes a crank type and a wobble plate type and the like besides the swash plate type. The swash plate type compressor is also classified into a variable capacity type and a fixed capacity type.
FIGS. 1 and 2 show a conventional fixed capacity type swash plate compressor.
As shown in the drawings, the swash plate type compressor 1 includes a front housing 10 in which a front cylinder block 20 is provided and a rear housing 10a which is coupled with the front housing 10 and in which a rear cylinder block 20a is provided.
In the front and rear housings 10 and 10a, there are respectively formed a discharge chamber 12 and a suction chamber 11 inside and outside a partition wall 13 corresponding to a refrigerant outlet hole and a refrigerant inlet hole of a valve plate 61 to be described below.
The discharge chamber 12 is formed with a first discharge chamber 12a which is formed inside the partition wall 13 and a second discharge chamber 12b which is formed outside the partition wall 13 so as to be isolated from the suction chamber 11 and to be communicated with the first discharge chamber 12a through a discharging hole 12c. 
That is, the refrigerant in the first discharge chamber 12a is contracted when passing through the discharging hole 12c having a small diameter and then expanded when moving to the second discharge chamber 12b. While the refrigerant is contacted and expanded, pulsation pressure is lowered, thereby reducing vibration and noise.
Meanwhile, a plurality of bolt holes 16 are formed in the circumferential direction of the suction chamber 11. Through the bolt holes 16, the front and rear housings 10 and 10a are coupled to each other by bolts 80 in the status that a plurality parts are assembled therein.
The front and rear cylinder blocks 20 and 20a are formed with a plurality of cylinder bores 21 therein. The pistons 50 are inserted into the cylinder bores 21 of the front and rear cylinder blocks 20 and 20a, which are correspondent to each other, so as to be linearly reciprocated, and the pistons 50 are coupled through shoes 45 to the circumference of the swash plate 40 which is inclinedly coupled to a drive shaft 30.
Therefore, the pistons 50 is interlocked with the swash plate 40 rotated together with the drive shaft 30, and thus reciprocated in the cylinder bores 21 of the front and rear cylinder blocks 20 and 20a. 
A valve unit 60 is disposed between the front and rear housings 10 and 10a and the front and rear cylinder blocks 20 and 20a. 
The valve unit 60 is formed with a valve plate 61 having the refrigerant inlet hole and the refrigerant outlet hole, and a suction lead valve 63 and a discharge lead valve 62 disposed at both side surfaces thereof.
The valve unit 60 is respectively assembled between the front and rear housings 10 and 10a and the front and rear cylinder blocks 20 and 20a. At this time, fixing pins 65 formed at both sides of the valve plate 61 are respectively inserted into fixing holes 15 formed at surfaces of the front and rear housings 10 and 10a and the front and rear cylinder blocks 20 and 20a opposite to each other, so that the valve unit 60 can be positioned at a place.
Meanwhile, a plurality of communication passage 22 are formed at the front and rear cylinder blocks 20 and 20a so that the refrigerant supplied to a swash plate chamber 24 provided between the front and rear cylinder blocks 20 and 20a can be flowed to the suction chamber 11. The second discharge chambers 12b of the front and rear housings 10 and 10a are connected to each other through a connecting path 23 passing through the front and rear cylinder blocks 20 and 20a. 
Accordingly, the inhaling and compressing of the refrigerant are simultaneously performed in the cylinder bores 21 of the front and rear cylinder blocks 20 and 20a according to the reciprocating of the pistons 50.
And a shaft supporting hole 25 for supporting the drive shaft 30 is formed at a center protion of the front and rear cylinder blocks 20 and 20a, and a needle roller bearing is provided in the shaft supporting hole 25 so as to rotatably support the drive shaft 30.
Meanwhile, at an upper outer surface of the rear housing 10a, there is formed a muffler 70 which functions to supply the refrigerant transferred from the evaporator to the compressor upon an intake stroke of the piston 50 and discharge the refrigerant compressed in the compressor 1 to the condenser upon a compression stroke of the piston.
Hereinafter, refrigerant circulating processes of the compressor 1 as described above will be described.
The refrigerant supplied from the evaporator is inhaled to a suction part of the muffler 70 and then supplied through a refrigerant inlet port 71 to the swash plate chamber 24 provided between the front and rear cylinder blocks 20 and 20a, and the refrigerant supplied to the swash plate chamber 24 is flowed to the suction chamber 11 of the front and rear housings 10 and 10a along the communication passage 22 formed at the front and rear cylinder blocks 20 and 20a. 
Then, the suction lead valve 63 is opened upon the intake stroke of the piston 50. At this time, the refrigerant in the suction chamber 11 is inhaled into the cylinder bore 21 through the refrigerant suction hole of the valve plate.
The refrigerant in the cylinder bore 21 is compressed upon the compression stroke of the piston 50. At this time, if the discharging lead valve 62 is opened, the refrigerant is flowed to the first discharge chamber 12a of the front and rear housings 10 and 10a through the refrigerant outlet hole of the valve plate.
Sequentially, the refrigerant flowed to the first discharge chamber 12a is discharged to a discharging part of the muffler 70 through the second discharge chamber 12b and the refrigerant discharging port 72 of the muffler 70, and then flowed to the condenser.
Meanwhile, the refrigerant compressed in the cylinder bore 21 of the front cylinder block 20 is discharged to the first discharge chamber 12a of the front housing 10, and flowed to the second discharge chamber 12b, and flowed to the second discharge chamber 12b of the rear housing 10a through the connecting path 23 formed at the front and rear cylinder blocks 20 and 20a, and then discharged to the discharging part of the muffler 70 through the refrigerant outlet port 72 together with other refrigerant remained therein.
However, the conventional compressor 1 has a problem that a suction volume efficiency of refrigerant is deteriorated by a loss due to inhaling resistance generated by the complicated refrigerant paths, a loss due to elastic resistance of the suction lead valve 63 upon the opening/closing of the valve unit 60 and the like.
Meanwhile, in order to reduce the loss caused by the elastic resistance of the suction lead valve 63, there has been provided Korean Patent Laid-Open No. 2003-47729 (entitled “Lubricating structure in fixed capacitance type piston compressor”). That is, in the above technology, a suction rotary valve in which a drive shaft is integrally formed without the suction lead valve is employed. Also in order to reduce the loss by the inhaling resistance, the refrigerant can be directly flowed from a rear side of the drive shaft to the cylinder bore through an inner side of the drive shaft.
In the case of the above-mentioned compressors, oil is mixed with the refrigerant in order to lubricate the driving parts (swash plate, shoes, pistons and the like) and a friction part.
Moreover, in Korean Patent Application No. 2005-74185 filed by the applicant, a passage is formed in a drive shaft to which a swash plate is inclined coupled so as to be rotated in a swash plate chamber in the compressor, so that refrigerant inhaled in the compressor can be flowed to a cylinder bore formed in a cylinder block. Inlet and outlet holes are formed at both side of the passage so as to be spaced apart at a distance.
Herein, the inlet hole of the passage is formed to perforate a hub of the swash plate and a side of the drive shaft, or formed at both sides of the drive shaft in the opposite direction. In the latter case, the inlet holes are formed to be spaced apart from each other so that one of them is not opposed to the other.
Further, the outlet hole of the passage is communicated with a inhaling passage of each cylinder bore, and formed at both sides of the drive shaft in the opposite direction so that the refrigerant is inhaled into each cylinder bore formed at both sides of the swash plate chamber at the same time when the drive shaft is rotated.
However, in the case of Korean Patent Laid-Open No. 2003-47729, there is a limitation in forming a refrigerant inhaling passage at a rear side of the drive shaft and increasing the size thereof. Therefore, it is difficult to secure the sufficient refrigerant inhaling passage. In the case of Korean Patent Application No. 2005-74185, since there is a limitation in increasing a size of the passage, the refrigerant inhaling resistance is increased. Further, since it is difficult to sufficiently lubricate the thrust bear, friction force at the thrust bearing is increased, thereby reducing its durability.